The present invention pertains to computer networks, and more particularly, to a method of transferring data at 100 Mb/s transfer rates over local area networks (LAN's) using unshielded twisted pair (UTP) wire media.
In the world of computers, pc and workstation users are requiring greater network bandwidths/higher speeds to carry more and more data over existing networks. The need for higher speed networks will grow even faster as desktop computers are equipped with the higher speed bus architectures that are being developed. Over the past ten years, desktop pc processing power has increased over a hundredfold. Over that same period, however, the data transmission speed of Ethernet LAN's has remained constant at 10 Mb/s. Network speeds are now a common bottleneck in a variety of key business application areas including database management, imaging, computer-aided design and network printing. On a typical 10 Mb/s Ethernet or Token-Ring network, it can take as long as 20 seconds to retrieve a single page of data depending upon network traffic. If 100 Mb/s networks were available, transfers would not be network limited and would take only one or two seconds for that same page of data.
Generally, for high speed data transfer in excess of 25 Mb/s over a LAN, data has been transferred using fiber optic media, coaxial cable, shielded wire or other specialized cable. For example, the fiber distributed data interface (FDDI) protocol is a common network protocol which operates using a fiber optic medium. FDDI has been available the longest of any high speed (100 Mb/s) network architecture, but it is still the costliest. Very few business users of computers have installed fiber optic cabling. In the United States it is estimated that approximately 80% of existing LAN users have "category 3" (voice grade) unshielded twisted pair wiring to interconnect desktop users. Such cables are usually configured in 25-pair bundles to accommodate future organizational growth.
The use of fiber optic media or shielded twisted pair (STP) wire for local area networking present various problems of their own. Most existing office buildings have an installed base of UTP wiring--not fiber optic cable or STP wire. Therefore, to utilize a fiber optic or STP network, assuming existing cable ducts have the space available, it would be necessary to specially install high quality cabling. This can be cost prohibitive. Yet if a LAN could be designed to operate at speeds of 100 Mb/s and work over Category 3 to Category 5 (data grade) UTP wire, users could easily switch to the higher speed network interface equipment using the existing cabling installation.
There has been some work done to increase the rate over which data can be transferred over installed twisted pair cabling. See for example U.S. Pat. No. 5,119,402 issued to Simon A. Ginzburg et al. for a Method and Apparatus for Transmission of Local Area Network Signals over Unshielded Twisted Pairs. However, in the prior art there has been no work which has sufficiently increased the speed of data transmission so that transmission over a four pair voice grade UTP wire network can rival the speed of data transmissions over fiber optic cabling. Some of the reasons for this are obvious. Unlike fiber optic cable or STP wire, UTP wire has greater radio-frequency (rf) emissions since it is unshielded. And, because the twist of the wire pairs does not provide perfect balance, there are also crosstalk and noise interference problems. And as speeds increase above 10 Mb/s these problems are exacerbated along with high frequency rolloff causing signal distortion that increases with the length of the wire runs. Yet, given these problems there are various proposals for new network topologies to send data over UTP wire at transmission rates of 100 Mb/s; the present invention represents the heart of one of those proposals. And, although the present invention could easily be adapted to operate over higher quality cable, such as STP, it has its greatest utility (in terms of economy) for existing UTP wired facilities.